I'll start:
August Underground 1-3
The All Night Long Series
Inside (french)
High Tension
The Human Centipede? (maybe? the premise was pretty whacked-out)
Turistas (at least for me)
Flowers of the Flesh and Blood (which has nothing on August Underground, imo)
A Serbian Film (or Sprski Film)
Cannibal Holocaust (duh)
Martyrs
Irreversible
That's all I got for now, kinda out of it today.
this is a pretty good list, but I think I have some additions
Audition
Tokyo Gore Police
Three extremes (especially dumplings, the first segment)
Ichi the killer (of course)
anything by Dario Argento
your list is pretty good though! I've seen all of them except for the All Night Long series, thank you for the tip!
Salo
sharehorror:
subconscious cruelty
aftermath
genesis
red room
red room 2
pinocchio 362 (not sure about the number)
boy meets girl
everything by olaf ittenbach
schoolgirl in cement
machine girl
meatball machine
grotesque
other kind of sick/sickening/soul crushing:
benny's video
funny games
white ribbon
cache
thirst
oldboy
sympathy for lady vengeance
sympathy for mister vengeance
battle royal
battle royal 2
men behind the sun 1-x
"laugh and the world laughs with you. Weep and you weep alone." - Dae-su Oh
Suicide Club
Inside (Dimension Extreme)
And a movie that will tear your heart apart: Girl Next Door (http://www.imdb.com/title/tt0830558/)
Gutterballs. It's almost more of a comedy, but it's basically meant to be an extra gory slasher-flick with real sex scenes (although I'm not sure if a certain rape-scene is real). It's a fantastic flick though if you can stomach seeing things like a fat transvestite's genitals cut open from the middle, seeing someone choke on a vagina, or getting a face waxed off etc... It's a really funny film no matter how gory it gets... so well made :)
It's a hilarious film and almost like a parody of slasher-films even though it is one itself, with an awesome and accurate 1980s "feel".
It's from the same guy made movies like Live Feed (which is a lot worse though and more of the type of film people are listing here). Check that out too. Here's a trailer for Gutterballs, it's a must see for any comedy and gore fan: http://www.youtube.com/watch?v=dFTUrABM6DE
--X-marks_the_spot--tume-X--
The Untold Story.
Caligula.
In a Glass Cage.
Cannibal Ferox.
The New York Ripper.
"You killed Captain Clown, YOU KILLED CAPTAIN CLOWN"-The Joker
Trash Humpers
---
"Knightley is a poor man's Portman." -monkeypunks
Niku Daruma (aka Tumbling Doll Of Flesh) is the Citizen Kane of torture-porn
If you think Pantera is good music, you married your cousin and your retarded son's name is Cletus
I'm shocked to see that nobody mentioned this one: Melancholie der Engel (2009).
Is on YouTube, btw. It's REALLY fcked up.